Server Workgroup Login Problem

We made a username and password (windows nt 4) for this guy who work for this company. He uses his own laptop (works for many companies) and when he tries to login to the domain he gets the error shown below. Does anyone know what could be causing this problem?

Oh hell I never use the wizard. It looks like you already have a computer account with that name or are only allowed a single login. Join a workgroup, change the computer name to something else, reboot then join to the domain again.